The present invention related generally to logic analyzer probes and more particularly to a high density logic analyzer probing system for mounting logic analyzer probes to a device under test.
Logic analyzer probes are used for acquiring multiple signals from probing points, circuit traces, processor buses and the like on a device under test (DUT). Probing points may take the form of square pin connectors mounted on the DUT that are connected to circuit elements or circuit traces. Various types of high, speed, controlled impedance connectors may also be mounted on the DUT for coupling multiple high speed signals to the logic analyzer. One such connector is called a MICTOR® connector, manufactured and sold by Tyco Electronics, Corp., Harrisburg, Pa. A MICTOR® connector has a plug and closely mating receptacle. The transmission lines in the plug and receptacle are contained in mating housings. The ends of the transmission lines extending from the bottom of the receptacle are bent at an angle to form contact pads for soldering to parallel rows of conductive pads on the surface of a circuit board DUT. The ends of the transmission lines at the other end of the receptacle form electrical contacts that mate with corresponding electrical contacts in the plug when the closely mating plug and receptacle are connected together. In most probing applications of microprocessor boards, multiple MICTOR receptacles are mounted on the circuit board. The mating MICTOR plugs are mounted on multi-channel logic analyzer probe heads. The transmission lines of the MICTOR plug are electrically coupled to center conductors of a multiple coaxial cable type ribbon cable. Electrical elements, such as resistors, may be inserted between the MICTOR plug and the coaxial cables to provide electrical isolation for the device under test. One drawback to the use of MICTOR connectors is the amount of space the connectors take up on the DUT.
To reduce the amount of space take up by MICTOR connector and other such connectors, connectorless logic analyzer probes were developed. The connectorless logic analyzer probe mounts directly to the electrical contacts pads on the DUT and does not require the use of MICTOR connectors. One such connectorless logic analyzer probe is the P6860 Logic Analyzer Probe, manufactured and sold by Tektronix, Inc, Beaverton Oreg. and described in U.S. Pat. No. 6,447,339. The P6860 probe has a non-conductive plastic-type housing in which are secured substrates having electrical contacts formed on the one of the substrate ends and exposed at one end of the housing. The electrical contacts are electrically coupled to passive and active circuitry on the substrates. A removable signal contact holder is mounted over the open end of the housing. The removable signal contact holder has parallel rows of elastomeric contacts that correspond to the electrical contacts on the ends of the substrates. The probe is positioned on the DUT with the elastomeric contacts engaging a corresponding pattern of electrical contact pads on the DUT. The housing has attachment screws mounted on the sides of the housing that engage a retention block. The retention block has a stiffener member enclosed in a housing having alignment flanges that extend though holes in the DUT adjacent to the electrical contact pads on the DUT. The retention block is positioned on the reverse side of the DUT under the electrical contacts. The retention block flanges engage features on the housing to align the elastomeric contacts of the probe with the electrical contact pads on the DUT. The screws are tightened into the retention block to secure the probe to the DUT. The P6860 is designed for electrical contact pad patterns on the DUT of 85 contacts per square inch.
Another type of connectorless logic analyzer probe are PCIExpress Bus probes, manufactured and sold by Tektronix, Inc. The PCIExpress Bus probes have machined mounting posts that are positioned adjacent to the parallel rows of electrical contact pads on the DUT. The mounting posts have a base with apertures formed therein that receive mounting pins. The mounting pins extend into holes formed in the DUT adjacent to the electrical contact pads. The mounting pins are soldered to the DUT to secure the mounting post to the DUT. The mounting posts have upwardly extending studs with threaded apertures formed therein. An interconnect strip is positioned between the mounting posts. The interconnect strip have electrical contacts, such as a cLGA c-clip, manufactured and sold by InterCon Systems, Inc., Harrisburg, Pa., that correspond to the pattern of electrical contact pads on the DUT. The PCIExpress Bus probes has an open housing structure with substrates mounted on either side of a central support member. The substrates have electrical contacts formed on the one of its end surfaces that are exposed at the bottom of the housing. Side members attached to the central support member secure the substrates in the housing. Each side member has a central bore that receives a screw for securing the housing to the mounting posts. The probe is positioned between the mounting posts with the electrical contacts on the substrates engaging corresponding electrical contacts in the interconnect strip. The housing screws are tightened to secure the probe to the DUT. The PCIExpress Bus probe is designed for electrical contact pad patterns on the DUT of 130 contacts per square inch.
A drawback to the above described connectorless probes is the possibility of over tightening the probe heads to the DUT. In the case of the P6860 Logic Analyzer Probe, over tightening can cause the fine wires in the elastomeric connectors to take a permanent set causing the intermittent connections between the substrate contacts and the contact pads on the DUT. Further, the substrates may be forced into the soft plastic of the removable signal contact holder which may cause damage to the substrates themselves. In the case of the PCIExpress Bus probes, over tightening can cause damage to the electrical contacts in the interconnect clip. Further, the interconnect strip is separate from the probe head and not retained in the probe head as is the case with the P6860 probe.
Another type of connectorless probe are the E5387A, E5390A and the E5394A soft touch probes manufactured and sold by Agilent Technologies Inc., Palo Alto, Calif. The soft touch probes have a plastic retention module having downwardly facing metallic studs that are mounted into holes formed adjacent to the parallel rows of electrical contact pads on the DUT. The metallic studs are soldered to the DUT to secure the retention module to the DUT with the retention modules extending completely around the periphery of the parallel rows of electrical contact pads. The soft touch probe head has a plastic housing in which are secured parallel substrates. One end of each substrate has micro spring-pin electrical contacts that mate with the parallel rows of the electrical contact pads on the DUT. The micro spring-pin electrical contacts are coupled to wires of electrical ribbon cables extending from the other end of the housing via passive circuit elements. Mounting screws extend down opposing sides of the housing and are screwed into threaded apertures in the retention module. The soft touch probes are designed for electrical contact pad patterns on the DUT of 128 contacts per square inch.
A drawback to the soft touch probes is the use of the retention module which surrounds the electrical contact pad pattern on the DUT. The retention module requires more board space than is required with the PCIExpress Bus probe and further requires greater separation between adjacent contact pad patterns. Additionally, the micro spring-pin electrical contacts are mounted to the substrates and require the probes to be sent to a service center for repair if a micro spring-pin contact is broken.
There is a continuing customer need to increase the higher density electrical contact patterns on DUTs. As the contact density increases per square inch there is a corresponding decrease in the separation between adjacent electrical contacts. This requires greater precision in placing the logic analyzer probes on the DUT. What is needed is a high density logic analyzer probing system that accurately positions a probe mounting fixture on a device under test for accurately positioning a high density logic analyzer probe to the device under test. The high density logic analyzer probing system should also provide a positive stop that prevents damage to electrical contacts on the high density logic analyzer probe. Further, the high density logic analyzer probing system should be adaptable for use with various thicknesses of circuit boards and allow for placing the high density logic analyzer probes opposite of each other on opposing sides of the circuit board.